CHAMACEA. 103 



the same characters as the other Cerithia, and has been separated 

 by some writers under the generic name Telescopium. Cerithium 

 Aluco, fig. 372. Mediterranean, East and West Indies, Coasts of 

 the Pacific, Gallapagos, Australia, &c. Some small species are 

 British. Fossils are numerous in the tertiary beds. 



CERVICOBRANCHIATA. Bl. The second order of Paracephalo- 

 phora Hermaphrodita, Bl. containing symmetrical patelliform 

 shells, divided into the families Retifera and Branchifera. 



CETOCIS. Montf. Fam. Orthocerata, Lam. and Bl. Placed by 

 De Blainville in his section of Belemnites, characterized as having 

 small folds at the apex. Ex. B. Penicillatus. 



CETOPIRUS. Ranz. Coronula Bal^naris, Auct. fig. 16. 



CHAM A. Auct. Fam. Chamacea, Lam. and Bl. — Descr. Ine- 

 quivalve, irregular, thick, foliaceous, attached by the umbo of the 

 lower and larger valve. External ligament placed in a groove, 

 following the curve of the umbones. Umbones spiral, coiled 

 round on the back of the valves ; hinge with a thick, crenated, 

 lengthened tooth, in one valve, entering a corresponding cavity in 

 the hinge margin of the other ; muscular impressions, two in each 

 valve, distinct, lateral. — Obs. The Linnsean genus Chama, in- 

 cluded the beautiful shells now called Tridacna. These are ex- 

 ceedingly different from the true Chama, being regular and 

 unattached. The Chama (Tridacna) gigas, when at its full age 

 and development, is the largest shell known. Specimens have 

 occurred weighing upwards of 500 lbs., and measuring two feet 

 across. Diceras may be known from Chama by the spiral horns 

 into which the umbones are produced ; Isocardia, by the regu- 

 larity of the shells, and it is hardly necessary to mention Spon- 

 dylus, which may be known by the triangular disc between the 

 umbones ; Cleidothserus, Stutch. which resembles Chama in 

 general form, has a separate bony appendage attached to the 

 hinge, and may, moreover, be distinguished by its elongated 

 muscular impression. Fig. 153, C. Lazarus. E. and W. Indies. 



CHAMACEA. Bl. The seventh family of the order Lamellibran- 

 chiata, Bl. containing the genera Chama, Diceras, Etheria, Tri- 

 dacna, Isocardia and Trigonia. 



